1. Yaniv Mordecai & Dov Dori
Methodologies in Information Systems Development Model-Based Protocol Engineering: Specifying Kerberos with Object-Process Methodology
My name is Yaniv Mordecai, I am a Ph.D. Candidate at the Technion – Israel Institute of Technology.
This talk presents theoretical and methodological foundations which are part of my Ph.D. research on model-based risk-oriented systems engineering.
My supervisor is Prof. Dov Dori from the Technion, at the moment a visiting Professor at MIT, and I would like to thank Prof Olivier de-Weck from MIT Engineering Systems Division for inviting me to MIT.
Yaniv Mordecai & Dov Dori
Technion – Israel Institute of Technology, Haifa, Israel
November 3, 2015

2. Multiple engineering professionals talk different languages
Mechanical Engineers
Civil Engineers
Electronics Engineers
Software Engineers
Model-Based Protocol Engineering
November 2015

3. What is a Model?
A physical, mathematical, or otherwise logical representation of a system, entity, phenomenon, or process (DoD 1998).
A representation of one or more concepts that may be realized in the physical world (Friedenthal, Moore, and Steiner 2009).
A simplified representation of a system at some particular point in time or space intended to promote understanding of the real system (Bellinger 2004).
An abstraction of a system, aimed at understanding, communicating, explaining, or designing aspects of interest of that system (Dori 2002).
A selective representation of some system whose form and content are chosen based on a specific set of concerns (Object Management Group 2010).
Source:
Model-Based Protocol Engineering
November 2015

4. Systems Engineering Languages
Systems Modeling Language – SysML
OMG Standard since 2007
Object-Process Methodology – OPM
OPM book published in 2002
ISO Standard as of Aug. 2014
(formally: Publically Available Specification)
OPM software: OPCAT, freely downloadable from
Along with papers and other resources
Model-Based Protocol Engineering
November 2015

5. The idea behind conceptual modeling
conceived reality
modeled reality
Object
Vehicle
is a
Aircraft
Is modeled by
is a
affects
Bus
Is modeled by
Energy
Replenishing
Gas Filling is
Is modeled by
affects
Car
Process
Using graphical symbols, the model expresses physical things – objects and processes – and relations among them.
Model-Based Protocol Engineering
November 2015

6. OPM Entities – the bricks: Things and States
Object: A thing that exists or might exist physically or informatically.
Objects are stateful:
Objects can have states
At each point in time a stateful object is
at one of its states - static, or
in transition between two states – undergoing change
Process: A thing that transforms an object.
Transforming an object is:
creating it,
consuming it, or
changing its state.
Object
State 1
State 2
Processing
Model-Based Protocol Engineering
November 2015

7. Compact Ontology: A Minimum Length OPM alphabet
OPM unifies the system’s structure and behavior throughout the analysis and design of the system within one frame of reference using a small alphabet:
Two types of things:
(1) stateful objects
(2) processes
Two families of links:
(1) structural links: connect objects with objects
(2) procedural links: connect processes with objects
Model-Based Protocol Engineering
November 2015

8. Hierarchical Decomposition Illustration
Model-Based Protocol Engineering
November 2015

9. ISO Standardization OPM is now approved ISO standard 19450.
ISO is meant to provide a basis for a new generation of model-based standards.
Official standards need formal semantics to ensure the standard’s consistency and integrity.
Several standards we’ve tested were found to include contradictions and ambiguities that could be avoided, had a model-based approach been used to author and specify the standard.
Model-Based Protocol Engineering
November 2015

10. Unblocking the Paradigm Shift
“Standards/protocols are not systems”
But they are processes, procedures, or sets of definitions, eventually pertaining to a system at some level.
“Standards should be solution-independent”
But their underlying semantics must be well defined.
You don’t have to design the system that implements the standard with OPM, but you know that it is well-defined thanks to OPM.
“Standards should be defined in natural language text rather than conceptual modeling languages”
But we want to make sure that the text is valid and verified.
OPM lets you generate semi-natural language text based on the model.
“You can’t capture everything in the standard with a model”
Right! Focus the model on the core procedural, functional, and/or structural aspects being standardized.
Model-Based Protocol Engineering
November 2015

11. Kerberos
Common, widely-accepted protocol for computer user and device authentication across insecure computer networks.
Based on trusted 3-rd party authentication service.
Invented and developed at MIT with the support of Microsoft, Google, Apple, Oracle, and others.
MIT Kerberos Consortium has not provided a well-formed model-based protocol representation.
Model-Based Protocol Engineering
November 2015

12. Why Kerberos It’s simple It’s standardized
It’s well known to domain professionals
It consists of several components, services, information objects, and processes.
Model-Based Protocol Engineering
November 2015

13. Kerberos Procedure
Model-Based Protocol Engineering
November 2015

14. UML Sequence Diagram of Kerberos
Model-Based Protocol Engineering
November 2015

15. UML Sequence Diagram of Kerberos
Model-Based Protocol Engineering
November 2015

16. UML Sequence Diagram of Kerberos
Model-Based Protocol Engineering
November 2015

17. Problems with the UML Sequence Diagram
Notation problems.
Mixture sequence diagram, activity diagram, and some informal diagram semantics.
Confusing use of rectangular blocks for different types of entities (processes and objects).
Extensive use of in-diagram free text.
Lack of capability to execute the visualized model.
The diagram does not show branches of the process, i.e., what happens when one of the subsequences fails.
The diagram captures only the first two levels of the internal processes conducted by each participant.
Model-Based Protocol Engineering
November 2015

18. Why Did Those Problems Occur?
UML has 13 different diagrams to capture various aspects, each highlighting a different aspect.
Each diagram has different notation for similar concepts (e.g. Use Case, Activity, Method, Process)
UML does not generate a formal textual specification.
Eventually, the analyst works for the model more than the model works for the analyst!
Model-Based Protocol Engineering
November 2015

19. Kerberos in OPM
Model-Based Protocol Engineering
November 2015

20. Summary Model-based approach to standard authoring.
Object-Process Methodology (ISO 19450) as a conceptual modeling framework for protocol specification.
OPM-based specification and simulation of Kerberos, a well-known protocol.
Model-Based Protocol Engineering
November 2015

21. Protocol Modeling Assignment
Model a formal procedure (a standard or a protocol) with Object-Process Methodology (OPM) – ISO for complex system and process modeling and simulation.
Model-Based Protocol Engineering
November 2015

22. Important Dates Preliminary submission Dec. 19, 2015, Sat, 23:59.
Preliminary version of report
Introduction and literature review.
Description of the protocol.
A preliminary high-level OPM model of your protocol.
Preliminary version of the model
Presentation Jan. 12, 2016, Tue, 10:30.
Final submission Feb. 27, 2016, Sat, 23:59.
Model-Based Protocol Engineering
November 2015

23. Assignment Grading MODULE TASK WEIGHT Assignment (77%)
Preliminary report
10%
Preliminary version of OPM model
Presentation
12%
Final report
15%
Final version of OPM model
30%
Coursework (23%)
Attendance
13%
Participation, involvement, and consultation
TOTAL
100%
Model-Based Protocol Engineering
November 2015

24. Submission Guidelines
All submissions are to be made through Moodle.
Submit your report in the form of an IEEE Conference Paper (up to 8 pages).
Submit your model file separately.
The report should contain at most 3-4 OPDs for introductory and impression purposes.
In the text, refer to model views and diagrams in the file.
Focus on the most relevant and applicable parts of the protocol or standard that you’re modeling.
Model-Based Protocol Engineering
November 2015

25. Modeling Guidelines
Build the OPM model iteratively, using the detail decomposition approach.
Keep your model executable – this is a mandatory and significant!
Make assumptions and abstractions, employ modeling patterns and techniques as you see fit. Record your decisions and references.
Find issues in the technical specification (two contradicting sequences of the stages of the procedure; mismatch between the total time required for the protocol to end, and the sum of minimal durations of the individual steps, unclear or ambiguous specification…). Use the model and reasonable assumptions to resolve them.
Your OPM model should eventually contain processes and subprocesses across at least four levels (0..3).
All processes must be connected to objects, states, or other processes.
All objects must be connected to processes (directly or through a state) or other objects.
Model-Based Protocol Engineering
November 2015

26. Further Reading
Alex Blekhman and Dov Dori, Model-Based Requirements Authoring. INCOSE 2011 – the 6th International conference on System Engineering. March, 2011.
Alex Blekhman and Dov Dori, Tesperanto – A Model-Based System Specification Methodology and Language. Proc. 23rd Annual INCOSE International Symposium, Philadelphia, PA, USA, June 24-27, 2013
Yaniv Mordecai and Dov Dori, Conceptual Modeling of System-Based Decision-Making. Proc. 24th Annual INCOSE International Symposium, Las Vegas, NV, USA, June 30 – July 3, 2014.
Juan Wachs, Boaz Frenkel, and Dov Dori, Operation room tool handling and miscommunication scenarios: An Object-Process Methodology conceptual model. Artificial Intelligence in Medicine, Nov
Yaniv Mordecai and Dov Dori, Model-Based Protocol Engineering: Specifying Kerberos with Object-Process Methodology. IEEE 28th Convention of Electrical and Electronics Engineers in Israel, Eilat, Israel, Dec
ISO/PDPAS Automation systems and integration — Object-Process Methodology
Model-Based Protocol Engineering
November 2015

27. Yaniv Mordecai, yanivmor@technion.ac.il
Questions:
Yaniv Mordecai,